1. low weight,
2. high strength,
3. wide processing range,
4. high accelerations of axis motions in order to
(a) achieve constant operational rates even at small radii or corners, and PA1 (b) achieve the highest possible overall operational rates even for very complex processing contours.
Almost any conceivable axis drive exists for laser cutters designed for processing planar materials. The most important three (3) drives are:
1. Table at rest, portal being moved in the x-direction while the tool support affixed on the z-axis is being moved in the y-direction,
2. Compound table for the x and y axes, the material in the laser beam being moved on said table and a z-axis which ensures the proper height of the tool above the workpiece.
3. Table moved in the x-direction underneath a portal or through a stable arm used to shift the y-axis with integrated z-axis.
All these designs incur a common problem:
Even though the actual tool is merely a light beam applied by optical devices (mirrors and lenses) of comparatively low inertia to the material and even though direct processing forces do not arise that would have to be absorbed by the machine frame, the known designs are fairly high in mass. Illustratively, machines with a working range of 3.times.2 m as a rule weigh between 5 and 10 metric tons. The heaviest parts which must be moved with designs using a compound table for that kind of a design weight up to 5 metric tons and, as regards the design with movable portal ("flying optics"), weigh between 500 and 1,000 kg.
Considering the movable portal design, these weights arise from two (2) main requirements:
1. The large portal span, and
2. The required strength to guide the tool support including the z-axis and the required optical devices with little vibration, accuratly and as high as possible an acceleration.
The drives, especially to move the portal in the x-direction, accordingly are very powerful. Motors, gear units and shafts must withstand very high loads. If simultaneously precision is demanded, new problems and substantial costs arise because low-play gear-units and motors responding precisely to even minute signals are very complex and, hence, costly in such sizes.
Nevertheless, the resulting costly and heavy machines still are substantially too inert at their maximum acceleration of about 0.5 g in many applications to economically make use of the available laser power, for instance when, for serial cutting of small parts, for artistic shapes for advertising, and for filigrees, very tight radii must be transited in rapid sequences, the possible cutting speeds frequently being about 20 m/min. At a maximum acceleration of about 0.5 g, only radii up to about 15 mm can be transited at full speed.
This magnitude however is more theoretical than practical, because the resulting stresses on all parts of the drive would cause substantial wear and hence long shutdown times and consequential expenditures, so that economical operation is frequently precluded, the more so that even this acceleration anyway is insufficient for adequately constant and simultaneously high speed in many cases (corners and small radii of about a few mm).
Similar conditions apply also to other processing modes, for instance high-speed milling of light metals, and for engraving or plotting equipment.